Polymerization of butadiene hydrocarbons in the presence of a trithiocarbonate



Patented Apr. 3, 1951 POLYMERIZATION OF BUTADIENE HYDRO-- CARBONS IN THE PRESENCE OF A TRI- THIGCARBONATE Edward S. Blake and John R. Durland, Nitro,

W. Va., assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application November 7, 1944, Serial No. 562,409

7 Claims. 1

The present invention relates to a process for the preparation of butadiene polymers. More particularly, the invention relates to rubber-like polymers of butadiene hydrocarbons.

Synthetic sulfur-vulcanizable polymers of butadiene compounds which resemble natural rubber are made, for instance, by polymerizing butadiene-1,3 in aqueous emulsion in the presence of suitable vinyl compounds copolymerizable therewith. It is well known that the quality and usefulness of the copolymers are determined largely by the substances present, along with the polymerizable components, during the polymerization process. A substance, usually an oxygen yielding substance, is added to promote the polymerization so that it can be completed within a reasonably short time at low temperature. Other auxiliary agents such as emulsifying agents and a material which exerts a regulating effect upon the polymerization are usually added. The pur-' pose of the regulating agent is to control the polymerization to obtain a polymer which more closely resembles unvulcanized natural rubber. Otherwise, the polymerization easily results in hard insoluble products which are more like vulcanized rubber than the unvulcanized variety. As a consequence, the polymer is difficult to mill activity increases with increasing pH so that the pH of the emulsion as well as the amount of regulator may be adjusted to give precisely the activity desired. While the polymerization may be conducted in alkaline, neutral or acid medium, best results with the new regulators are obtained at pH 7-115.

Typicalexamplesof aryl methyl esters of thiol acids which may be used in the practice of this invention comprise di-(B-naphthyl methyl) trithiocarbonate, B-naphthyl methyl ethyl xanthate, benzyl trithiocarbonates, as for example benzyl ethyl trithiocarbonate, o-chlor benzyl ethyl trithiocarbonate, p-chlor benzyl butyl trithiocarbonate, o-chlor benzyl butyl trithiocarbonate, benzyl isopropyl trithiocarbonate, dibenzyl trithiocarbonate, di-(p-chlor benzyl) trithiocarbonate, trichlor benzyl n-butyl trithiocarbonate, be-nzyl amyl trithiocarbonate, dichlor benzyl butyl trithiocarbonate and di-(dichlor benzyl) trithiocarbonate. Other suitable compounds are di-(S-benzyl) dithiocarbonate, benzyl benzyl 5 xanthate, S-benzyl ethyl monothiocarbonate, S-

and compound. It is therefore common practice i to adda regulating agent to a butadiene emulsion before the polymerization step.

Among the objects of this invention is to provide a new class of regulating agents. A particular object of the invention is to provide a class.

of regulating agents which under a variety of conditions consistently control the polymerization of butadiene compounds so that products closely resembling unvulcanized natural rubber are produced. Another object is to provide a class of regulating agents which can be prepared easily and cheaply. Other objects will be apparent from the detailed description following.

In accordance with this invention it has been discovered that aryl methyl esters of thiol acids exert a remarkable regulating effect upon the course of the polymerization of butadiene compounds. They control the polymerization so that plastic easily worked polymers are produced. A

small proportion based on the monomeric constituents is sufiicien't and" exerts a marked effect on the polymerization. Less than 1.0% is usu-"' ally sufiicient and in general 02-05% give opti-'-- mum results. The pH of the emulsion affects the activity-of the new regulators. For instance, the

benzyl butyl monothiocarbonate, benzyl diethyl dithiccarbamate, benzyl diamyl dithiocarbamate, the benzyl ester of benzothiolic acid and chlor benzyl esters of benzothiolic acid, benzyl thiol acetate and dibenzyl thiol phthalate.

The new process can be applied to the polymerization of substituted butadiene-l,3as wellas to butadienel,3 itself as for example, isoprene,

2,3'-dimethyl butadiene and piperylene includ ing mixtures of butadiene-LS compounds with polymerizable mono-olefines containing the structure jexamplesillustrate the inveniqnbutths'.lnyentionis by no an li d thereto. I

-Benzyl tr-ithiocarbonates were employed as regulating agents for the polymerization of butadiene-1,3 and styrene in aqueous emulsion at a pH of about 7.3. The charge was as follows:

Parts by weight Butadiene '75. Styrene 30. Water 261. Potassiumpersulfate L 0.52 Y Decyl benzene sodium s'ulfonate 4.7 NaH2PO4 Ha2HPO4 3.82

Tab L Per Cent Firestone ggg qe Regulating Agent 35se -mers Seconds None I 500 0.5 Di-(o-chlor benzyl) trithiocarbonate 94 0. 3 Benzyl n-butyl trithiocarbonate. 84

O. 2 Benzyl methyl trithio'carbcnat 44' 0. 5 Di-(phcnyl chlor methyl) t1 itmocarbona 92 0.5 oGhlor benzyl n-butyl trithio carbonate.

Butadiene and styrene were polymerized in aqueous emulsion at a pI-I of about aempmymg aryl methyl esters of thio' acids as: regulating agent. The arge consisted of." l

Hart by We ht Butadiene-l,3 11 2.5 Styrene 31.5 Water 2 2 5 Potassium persulfate 1.5 Ivory Snow 4.5

A small proportion based on the total monomers present of re ulat'ng" gent 'was'addedjto the emulsion andpolyineriz 16.111 carried out byheatimg and stirring theaboi'ejcharge in a gns 1m autoclave 22 hours at5'0 C, aiti; which the polymer was coagulated and dr ed' 'G'QQdi yielj s. oifrubbery cop'olymer', were obtained. Plasticiti 1' were" determined on] a Eirestone extrus'tion plastometer asde'scribed above. The table below sets forth W15 1 t iWQ U Ob d y 3. of thene w regulating agents.

ble. I,

Per Cent Based on- Monomers Regulating ent Flaw-c ity Secohds None D -(o-chlor benzyl); trithiocarbonate; Dl-benzyl trithiocarbonate Benzyl ethyl xanthate Benzyl carbethQx-y trithiocarbonate. D -(trichlor benzyl) trithiocarbonate. D1;(B na'phthyl methyl) trithiocarbonate Tnchlor bcnzyl-ester of ,benzothiolic 'ac Banv yl ester ofbenzethiolic acid S-Tnchlor benzyl, ethyl monothioca S-Benzyl, ethyl monothiocarbonate: Trlchlor henzylldiethyl :djthiocarbamate. I a Naphthyl ethyl-*xanthate Butadiene and. styrene were conolymerizeq n Firestone aqueous emulsion at a pH of about 11.5. The charge was as follows:

Parts by weight Butadiene-1,3 112.5 Styrene 37.5 Water 225. Potassium persulfate 1.5 Ivory Snow L 4.5 Sodium hydroxide 1.15

Substantially 0.3% based on the total monomers present of di-(o-chlor-benzyl) trithiocarbonate was'auded to the emulsion. This emulsion was stirred anfd heated in a glass lined autoclave 22 hours at 50 C. The latex of the copolymer was then coagulated and the rubbery coagulum dried. lhe yield ofcopolymer was about based on the" monomers charged and the plasticity measured on a Firestone extrusion plastometer 6 secends.

"The present invention allows the manufacture of synthetic sulfur-vulcanizable butadiene polymers which can be processed in the factory in a 1112 1 6 3 similar #9, that followed for processing natural rubber in'the manufacture of rubber al ticles. Obviously, many variations can be made in the specific formulas set forth to illustrate the invention without departing from the spirit or scope or the present invention. The present invention is limited solely by the claims attached hereto as part ofthe present specification.

' What is claimed is: V

1. The process of regulating polymerization which ise pol m r i a m o eric mi ture containing butadienelfi and styrene in the form 0t an aqueous emulsion in the presence of 0.3-0.5% based on the total monomers present of a benzyl trithiocarbonate possessin the strucl re 0 ,115 C 1111? C s -R where, m is a number less than four and R is an alkyl radicle. l

2. The process of v regulating. polymerization which comprises polymerizing a monomeric mixture containing butadiene lfi and: styrene in the form of an aqueous. emulsion in the, pres; enoe of 0.3 0.5.% based on the total monomers li en f. a e l tr h ea eee e mss ssi s the structure mers present of di- (o chlor-loenzyl) trithiocar bonate.

4;. The process of regulating pgflymerizatior which comprises polymerizing a monomeric. mixture containing butadiene-1,3 and tyrene in emulsion form in the presence ofan efiective amount less than 1% based on the total mono: mers present, of benyl butyl trithiocarbonate.

5, The process of; regulating polymerization which comprises polymerizing a monomeric ixt re o ta m' u e rm. an rene in emulsion form in. thepresence of. an effiectiye amount less than 1% based. on thetotal. mono mers present of dibenzyl trithiocarbonate.

e. P ces o re la n p lym riz ti n. whic c mp s po ymeri n av monomeric.

mixture containing a butadiene-1,3 hydrocarbon and styrene in the form of an aqueous emulsion in the presence of an effective amount less than 1% based on the total monomers present of a trithiocarbonate possessing the structure s RSgS-R where R represents an aromatic substituted methyl radical, where R represents a radical selected from the roup consisting of alkyl radicals and aromatic substituted methyl radicals, and where said aromatic substituents consist solely of the elements selected from the group consisting of carbon, hydrogen, and chlorine.

7. The process of regulating polymerization which comprises polymerizing a monomeric mixture containing butadiene-1,3 and styrene in the form of an aqueous emulsion in the pres ence of an eifective amount less than 1% based on the total monomers present of a trithiocarbonate possessing the structure where R represents an aromatic substituted methyl radical, where said aromatic substituent consists solely of the elements selected from the group consisting of carbon, hydrogen, and chlorine, andwhere m represents a number less than four. I

EDWARQ S. BLAKE. JOHN R. DURLAND.

REFERENCES CITE]? The following references are of :record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Concise Chemical and Technical Dictionary (Bennett), Chem. Pub. Co. 1947, pp. ix, xix, and 76.

Snyder et al., J. Am. Chem. Soc., vol. 68, Aug. 1946, pp. 1422, 1426 and 1427. 

6. THE PROCESS OF REGULATING POLYMERIZATION WHICH COMPRISES POLYMERIZING A MONOMERIC MIXTURE CONTAINING A BUTADIENE-1,3 HYDROCARBON AND STYRENE IN THE FORM OF AN AQUEOUS EMULSION IN THE PRESENCE OF AN EFFECTIVE AMOUNT LESS THAN 1% BASED ON THE TOTAL MONOMERS PRESENT OF A TRITHIOCARBONATE POSSESSING THE STRUCTURE 